1. Technical Field
The present invention is directed to the art of RF power amplifier systems suitable for use in RF broadcast transmission systems and, more particularly, to improvements for such amplifier systems to be operated in different power control modes.
2. Description of the Prior Art
RF power amplifiers are known in the art and are used in Radio and Television broadcast applications. Such amplifiers may need to be operated in different power control modes, such as automatic level control (ALC), automatic gain control (AGC) or manual gain control (MGC). In the ALC mode, the output power of the power amplifier is proportional to the ALC reference; and it does not have a direct relationship to the input power. In the AGC mode, the output power is proportional to the input power. In the MGC mode, the output power is directly related to a signal that may be applied to a gain control device, such as an attenuator.
It is desirable that such an RF power amplifier be easily configured so that it can operate in either of the ALC or AGC or MGC modes. This will permit the same RF power amplifier configuration to be used in different applications. For example, the same amplifier could be used as a basic power unit at a final amplification stage or it could be used as an RF driver or a preamplifier in an overall power amplification system. If the power amplifier is used as a driver, instead of operating in ALC mode, it may be desirable to operate in either an AGC or in an MGC mode to work inside of an overall ALC loop. Since most traditional RF amplifiers use hardware to implement the power control loop, there is no easy way to switch the control mode or change the gain during operation. Consequently, the amplifier could be operated only in one of the three different modes without making changes to hardware.